Hydraulic pressure producing system for automatic transmission and control method thereof

ABSTRACT

A hydraulic pressure producing system for an automatic transmission, and a control method thereof may include a first hydraulic pump adapted to generate hydraulic pressure for shifting, a second hydraulic pump adapted to additionally generate hydraulic pressure when hydraulic pressure supplied from the first hydraulic pump is insufficient, an accumulator adapted to store hydraulic pressure excessively generated from the first hydraulic pump, and a control unit controlling the second hydraulic pump. The method may include operating the first hydraulic pump in a state of idle stop, predicting a finish point of the idle stop state, starting operation of the second hydraulic pump prior to a predetermined time from the predicted finish point, operating the second hydraulic pump with a predetermined maximum rotation speed, and operating the second hydraulic pump with a target rotation speed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2011-0134872 filed in the Korean Intellectual Property Office on Dec. 14, 2011, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydraulic pressure producing system for an automatic transmission and a control method thereof. More particularly, the present invention relates to a hydraulic pressure producing system for an automatic transmission and a control method thereof for improving energy efficiency.

2. Description of Related Art

Generally, the term “electric vehicle” represents all the vehicles that move by an electric power.

A hybrid vehicle is a vehicle with combined functions of a gasoline vehicle and an electric vehicle in order to overcome drawbacks of the gasoline vehicle and the electric vehicle. Therefore, a driver of a hybrid vehicle can select a gasoline engine drive mode or an electric motor drive mode.

Among transmissions, a continuously variable transmission or an automatic transmission is widely used in a hybrid vehicle. Particularly, the automatic transmission includes a number of frictional elements for performing multi-stage shifting. The frictional elements are operated by hydraulic pressure.

Meanwhile, the automatic transmission is connected to a mechanical hydraulic pump and an electric hydraulic pump so as to generate hydraulic pressure for shifting. In addition, the electric hydraulic pump additionally supplies hydraulic pressure to the automatic transmission when hydraulic pressure supplied by the mechanical hydraulic pump is not sufficient for shifting. That is, the electric hydraulic pump selectively generates hydraulic pressure by necessity.

According to hydraulic pressure generating in the electric hydraulic pump, the electric hydraulic pump is operated at a low RPM that is predetermined based on a state of idle stop for improving responsiveness. Herein, the idle stop is the condition in which power of the engine is not transmitted to the automatic transmission. In other words, the electric hydraulic pump is always operated while the vehicle drives although the RPM of the electric hydraulic pump may be different according to the vehicle driving conditions. Therefore, electric power is consumed by the electric hydraulic pump even in the state of idle stop in which hydraulic pressure generated in the electric hydraulic pump is not required. That is, electric power may be unnecessarily consumed.

In addition, hydraulic pressure that is excessively generated from the mechanical hydraulic pump while the vehicle drives is required to be recycled.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing a hydraulic pressure producing system for an automatic transmission and a control method thereof having advantages of preventing electric power from being unnecessarily consumed.

In addition, various aspects of the present invention are directed to providing a hydraulic pressure producing system for an automatic transmission and a control method thereof having advantages of improving fuel consumption by recycling excessively generated hydraulic pressure.

In an aspect of the present invention, a control method of a hydraulic pressure producing system for an automatic transmission, the hydraulic pressure producing system having a first hydraulic pump adapted to generate a first hydraulic pressure for shifting, a second hydraulic pump adapted to additionally generate a second hydraulic pressure when the first hydraulic pressure supplied from the first hydraulic pump is insufficient fir shifting, an accumulator adapted to store hydraulic pressure excessively generated from the first hydraulic pump, and a control unit controlling the second hydraulic pump, may include operating the first hydraulic pump in a state of idle stop, predicting a finish point of the state of the idle stop, starting operation of the second hydraulic pump prior to a predetermined time from the predicted finish point, operating the second hydraulic pump with a predetermined maximum rotation speed, and operating the second hydraulic pump with a target rotation speed after the second hydraulic pump is operated with the predetermined maximum rotation speed.

A generated hydraulic pressure of the second hydraulic pump is increased to more than a target hydraulic pressure when the second hydraulic pump is operated with the predetermined maximum rotation speed.

Hydraulic pressure stored in the accumulator is used to shorten a time in which the generated hydraulic pressure is increased.

In another aspect of the present invention, a hydraulic pressure producing system for an automatic transmission, may include a first hydraulic pump adapted to generate a first hydraulic pressure for shifting, a second hydraulic pump adapted to additionally generate a second hydraulic pressure when the first hydraulic pressure generated by the first hydraulic pump is insufficient for shifting, a control unit controlling the second hydraulic pump, and an oil tank fluid-connected to the first and second hydraulic pumps and supplying oil to the first hydraulic pump and the second hydraulic pump, wherein the control unit predicts a finish point of an idle stop state and operates the second hydraulic pump prior to a predetermined time from the predicted finish point when the first hydraulic pump is operated in the idle stop state.

The first hydraulic pump is a mechanical hydraulic pump.

The second hydraulic pump is an electric hydraulic pump having a motor.

The control unit controls operation of the motor so as to control rotation speed of the second hydraulic pump.

In further another aspect of the present invention, a hydraulic pressure producing system for an automatic transmission, may include a first hydraulic pump supplying a first hydraulic pressure for shifting to the transmission, a second hydraulic pump selectively supplying a second hydraulic pressure to the transmission, an accumulator fluid-connected to the first hydraulic pump and the second hydraulic pump and storing hydraulic pressure excessively generated by the first hydraulic pump and selectively transmitting the stored hydraulic pressure to the transmission, a control unit controlling operation of the second hydraulic pump, and an oil tank fluid-connected to the first hydraulic pump and the second hydraulic pump and supplying oil to the first and second hydraulic pumps, wherein the control unit determines a starting point for operating the second hydraulic pump, and wherein hydraulic pressure of the accumulator and the second hydraulic pressure of the second hydraulic pump are transmitted to the transmission when the second hydraulic pump is operated.

The second hydraulic pump is an electric hydraulic pump having a motor.

The control unit controls operation of the motor so as to control rotation speed of the second hydraulic pump.

The control unit predicts a finish point of an idle stop state and operates the second hydraulic pump prior to a predetermined time from the predicted finish point when the first hydraulic pump is operated in the idle stop state.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hydraulic pressure producing system for an automatic transmission according to an exemplary embodiment of the present invention.

FIG. 2 is a graph illustrating the RPM of the second hydraulic pump and the generated hydraulic pressure according to an exemplary embodiment of the present invention.

FIG. 3 is a flowchart of a control method of a hydraulic pressure producing system for an automatic transmission according to an exemplary embodiment of the present invention.

FIG. 4 is a block diagram of members for predicting a finishing point of the idle stop according to an exemplary embodiment of the present invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a hydraulic pressure producing system for an automatic transmission according to an exemplary embodiment of the present invention.

As shown in FIG. 1, a hydraulic pressure producing system 10 for an automatic transmission 60 according to an exemplary embodiment of the present invention includes a first hydraulic pump 20, a second hydraulic pump 30, valves 70, a motor 32, a control unit 34 and an accumulator 40.

The first hydraulic pump 20 generates hydraulic pressure for shifting. In addition, the first hydraulic pump 20 pumps oil supplied from an oil tank 50 so as to transmit oil to the transmission 60. Further, the one of the valves 70 is disposed between the first hydraulic pump 20 and the transmission 60. The first hydraulic pump 20 may be a mechanical hydraulic pump.

The second hydraulic pump 30 additionally generates hydraulic pressure when hydraulic pressure generated by the first hydraulic pump is insufficient. The second hydraulic pump 30 pumps oil supplied from the oil tank 50 so as to transmit oil to the transmission 60. In addition, the other one of the valves 70 is disposed between the second hydraulic pump 30 and the transmission 60. The valves 70 are check valves for passing oil only toward the transmission 60. The second hydraulic pump 30 is not operated while a state of idle stop is maintained. The idle stop state is a state in which a power of an engine is not transmitted to the automatic transmission 60. Further, the second hydraulic pump 30 starts to operate prior to a predetermined time from a point that the idle stop state is finished. Herein, the predetermined time is easily determined by a person of ordinary skill in the art.

The motor 32 is mounted at the second hydraulic pump 30. That is, the second hydraulic pump 30 is an electric hydraulic pump to perform pumping by operation of the motor 32.

The control unit 34 controls the pumping of the second hydraulic pump 30. The control unit 34 may be a motor control unit (MCU) that controls the operation of the motor 32. The motor 32 is controlled by the control unit 34 such that the RPM of the second hydraulic pump 30 is controlled.

The accumulator 40 stores hydraulic pressure that is excessively generated by the first hydraulic pump 20. Hydraulic pressure stored in the accumulator 40 is selectively supplied to the transmission 60.

Referring to FIG. 2 to FIG. 4, a control method of a hydraulic pressure producing system for an automatic transmission according to an exemplary embodiment of the present invention will be described in detail.

FIG. 2 is a graph illustrating the RPM of the second hydraulic pump and the generated hydraulic pressure according to an exemplary embodiment of the present invention. In addition, FIG. 3 is a flowchart of a control method of a hydraulic pressure producing system for an automatic transmission according to an exemplary embodiment of the present invention. Further, FIG. 4 is a block diagram of members for predicting a finishing point of the idle stop according to an exemplary embodiment of the present invention.

If the first hydraulic pump 20 is operated at the idle stop state at step S100, an electronic control unit (ECU) 100 predicts a finish point of the idle stop state at step S110. A signal is transmitted from a sensor 90 detecting operations of a brake 80 and a brake pedal 82 to the ECU 100 for predicting the finish point of the idle stop state.

If the finish point of the idle stop state is predicted, operation of the second hydraulic pump 30 is started prior to a predetermined time from the predicted finish point at step S120. Herein, the predetermined time is easily determined by a person of ordinary skill in the art.

If the operation of the second hydraulic pump 30 is started, the second hydraulic pump 30 is operated with a predetermined maximum RPM V1 for a predetermined time at step S130. In addition, a generated hydraulic pressure is increased to more than a target hydraulic pressure P in the step S130. The target hydraulic pressure P is a value of hydraulic pressure demanded for shifting. The generated hydraulic pressure of the step S130 may be the sum of hydraulic pressure generated from the second hydraulic pump 30 and hydraulic pressure supplied from the accumulator 40. The hydraulic pressure stored in the accumulator 40 may be used in the step S130. Therefore, a time T from the finish point of the idle stop state to a point that the generated hydraulic pressure reaches the target hydraulic pressure P is decreased compared to a case of using only the second hydraulic pump 30. In addition, the predetermined maximum RPM V1 is determined to be low compared to the case of using only the second hydraulic pump 30.

The second hydraulic pump 30 is operated with a target RPM V2 at step S140 after the second hydraulic pump 30 is operated with the predetermined maximum RPM V1 while the predetermined time passes. At this time, the second hydraulic pump 30 generates the target hydraulic pressure P. In addition, a generated hydraulic pressure of the step S140 is hydraulic pressure generated from the second hydraulic pump 30. That is, hydraulic pressure stored in the accumulator 40 is not used.

According to an exemplary embodiment of the present invention, the electric power is not unnecessarily consumed in the idle stop state. In addition, fuel consumption can be improved since hydraulic pressure that is excessively generated by the first hydraulic pump 20 is recycled. Furthermore, noise generated from a hydraulic pressure producing system 10 for an automatic transmission can be reduced.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

What is claimed is:
 1. A control method of a hydraulic pressure producing system for an automatic transmission, the hydraulic pressure producing system having a first hydraulic pump adapted to generate a first hydraulic pressure for shifting, a second hydraulic pump adapted to additionally generate a second hydraulic pressure when the first hydraulic pressure supplied from the first hydraulic pump is insufficient fir shifting, an accumulator adapted to store hydraulic pressure excessively generated from the first hydraulic pump, and a control unit controlling the second hydraulic pump, the method comprising: operating the first hydraulic pump in a state of idle stop; predicting a finish point of the state of the idle stop; starting operation of the second hydraulic pump prior to a predetermined time from the predicted finish point; operating the second hydraulic pump with a predetermined maximum rotation speed; and operating the second hydraulic pump with a target rotation speed after the second hydraulic pump is operated with the predetermined maximum rotation speed.
 2. The method of claim 1, wherein a generated hydraulic pressure of the second hydraulic pump is increased to more than a target hydraulic pressure when the second hydraulic pump is operated with the predetermined maximum rotation speed.
 3. The method of claim 2, wherein hydraulic pressure stored in the accumulator is used to shorten a time in which the generated hydraulic pressure is increased.
 4. A hydraulic pressure producing system for an automatic transmission, comprising: a first hydraulic pump adapted to generate a first hydraulic pressure for shifting; a second hydraulic pump adapted to additionally generate a second hydraulic pressure when the first hydraulic pressure generated by the first hydraulic pump is insufficient for shifting; a control unit controlling the second hydraulic pump; and an oil tank fluid-connected to the first and second hydraulic pumps and supplying oil to the first hydraulic pump and the second hydraulic pump, wherein the control unit predicts a finish point of an idle stop state and operates the second hydraulic pump prior to a predetermined time from the predicted finish point when the first hydraulic pump is operated in the idle stop state.
 5. The system of claim 4, wherein the first hydraulic pump is a mechanical hydraulic pump.
 6. The system of claim 4, wherein the second hydraulic pump is an electric hydraulic pump having a motor.
 7. The system of claim 6, wherein the control unit controls operation of the motor so as to control rotation speed of the second hydraulic pump.
 8. A hydraulic pressure producing system for an automatic transmission, comprising: a first hydraulic pump supplying a first hydraulic pressure for shifting to the transmission; a second hydraulic pump selectively supplying a second hydraulic pressure to the transmission; an accumulator fluid-connected to the first hydraulic pump and the second hydraulic pump and storing hydraulic pressure excessively generated by the first hydraulic pump and selectively transmitting the stored hydraulic pressure to the transmission; a control unit controlling operation of the second hydraulic pump; and an oil tank fluid-connected to the first hydraulic pump and the second hydraulic pump and supplying oil to the first and second hydraulic pumps, wherein the control unit determines a starting point for operating the second hydraulic pump, and wherein hydraulic pressure of the accumulator and the second hydraulic pressure of the second hydraulic pump are transmitted to the transmission when the second hydraulic pump is operated.
 9. The system of claim 8, wherein the second hydraulic pump is an electric hydraulic pump having a motor.
 10. The system of claim 9, wherein the control unit controls operation of the motor so as to control rotation speed of the second hydraulic pump.
 11. The system of claim 9, wherein the control unit predicts a finish point of an idle stop state and operates the second hydraulic pump prior to a predetermined time from the predicted finish point when the first hydraulic pump is operated in the idle stop state. 